<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        
    </style>
</head>
<body>
    
</body>
<script>

    var str = "hello js";
    console.log(str);
    console.log(str);
    console.log(str);


    var a = 10;
    var b = a;
    console.log(a)
    console.log(b)
    b = 20
    console.log(b)

    var c,d;
    console.log(c)
    console.log(d)

    var e,f=30,g;
    console.log(e)
    console.log(f)
    console.log(g)

    var h = null;
    console.log(h);

    // var var = "hahaha"

    
</script>
</html>